Project crashing calculator — free, and it does the trade-off for you

Crashing a project means buying time with money: you pay overtime, add a second crew, or bring in a subcontractor so a task finishes sooner. The arithmetic looks easy and almost nobody gets it right by hand, because the cheapest task to shorten is usually not the one worth shortening — and the critical path moves the moment you shorten anything on it.

Open the scheduler and crash a plan

Free, no signup. Upload the Excel template or start from the sample.

The part people get wrong

The textbook method is: find the critical path, pick the activity with the lowest cost slope, shorten it by one day, repeat. That is correct, and it is also exactly where hand calculation falls apart. After one or two days of crashing, a different path becomes critical — often two paths become critical at once — and from that point on you have to shorten a task on every critical path simultaneously or the project end date does not move at all. You paid for overtime and bought nothing.

That is the real reason crashing belongs in a solver rather than a spreadsheet. The solver is not doing anything you could not do with enough patience; it is doing the bookkeeping on which paths are critical after each decision, which is the part that is easy to get wrong and impossible to check by eye.

Cost slope, the one number you need per task

For each task that can be shortened, the cost slope is:

• Normal duration and normal cost — what it takes and costs at ordinary pace.
• Crash duration and crash cost — the shortest it can possibly run, and what that costs.
• Cost slope = (crash cost − normal cost) ÷ (normal duration − crash duration). Dollars per day saved.

Two honest cautions. A task with no crash duration listed cannot be crashed at all — concrete cures in the time concrete cures, whatever you spend. And a cost slope is rarely linear in real life: the second crew is cheaper per day than the fourth, because the fourth is tripping over the other three.

What this tool actually does

• Finds the critical path first, with crew constraints applied — a task can be critical because you only have two electricians, not because of the logic.
• Given a target finish date, chooses which tasks to crash and by how much, for the lowest total cost, keeping every dependency intact.
• Recomputes criticality after each decision rather than assuming the first critical path stays critical.
• Shows you the cost curve: what one day earlier costs, and what the fifth costs, which is usually where the argument with the client actually happens.

What it does not do

It does not model quality or risk. Crashing genuinely increases the chance of rework — more people on a tighter schedule is how mistakes get made — and no cost slope captures that. Treat the output as the money answer, not the whole answer. It also does not do fast-tracking, which is a different lever: overlapping tasks that were planned in sequence. Fast-tracking changes the network; crashing changes durations.

Common questions

What is the difference between crashing and fast-tracking? Crashing shortens a task by spending money on it. Fast-tracking runs two tasks in parallel that you had planned one after the other, which costs nothing directly but adds risk, because the second task starts on incomplete information.

Which tasks should I crash first? Only tasks on the critical path — shortening anything else buys nothing — and among those, the lowest cost slope first. But re-check criticality after every step, because that is where hand methods go wrong.

Can crashing ever fail to shorten the project? Yes, routinely. Once two paths are critical, shortening a task on one of them leaves the other path setting the finish date. You pay and the date does not move.

Do I need the Excel template? It is the easiest way in — grab the free Gantt chart template, fill in the tasks, and upload it. Or press the sample button and crash a plan that is already there.